Limited life medium

Abstract

A limited-life storage medium comprises a flowable agent. The flowable agent comprises water and a hygroscopic substance. In one example, the flowable agent is a mixture of glycol and water with an acid or other corrosive active ingredient dissolved in it. In one example, the storage medium is an optical disc. When the disc is read, the rotation of the disc propels the flowable agent into contact with a metal data-carrying layer. In one example, the hygroscopic substance reduces any tendency of the flowable agent to dry out and cease to be flowable, and may tend to buffer the proportion of water in the flowable medium within a range.

1 . A limited-life storage medium comprising a flowable agent, wherein the flowable agent comprises water and a hygroscopic substance. 
   
   
       2 . A limited-life storage medium according to  claim 1  that is arranged to be moved during reading, and wherein the flowable agent is arranged to move relative to the storage medium in response to the movement of the storage medium during reading to a position in which the flowable agent initiates a process limiting the operating life of the storage medium. 
   
   
       3 . A limited-life storage medium according to  claim 2  that is a disc, and wherein the flowable agent is arranged to move by centrifugal force in response to rotation of the disc during reading. 
   
   
       4 . A limited-life storage medium according to  claim 1  that comprises a metallic data-carrying element soluble in the flowable agent. 
   
   
       5 . A limited-life storage medium according to  claim 1  wherein the hygroscopic substance is flowable. 
   
   
       6 . A limited-life storage medium according to  claim 1  wherein the hygroscopic substance comprises at least one substance selected from the group consisting of ethylene glycol, propylene glycol, other glycols, glycerin, glycerols, silicones, and mixtures thereof. 
   
   
       7 . A limited-life storage medium according to  claim 6  wherein the hygroscopic substance comprises propan-1,2-diol. 
   
   
       8 . A limited-life storage medium according to  claim 7  wherein the flowable agent consists essentially of propan-1,2-diol, water, and at least one water-soluble reagent that in operation reacts with a data-carrying component of the medium so as to render at least a part of the data-carrying component unusable after a predetermined time. 
   
   
       9 . A limited life storage medium according to  claim 8 , wherein the ratio of propan-1,2-diol to water is at least 1:1 by volume. 
   
   
       10 . A limited life storage medium according to  claim 9 , wherein the ratio of propan-1,2-diol to water is at least 2:1 by volume. 
   
   
       11 . A limited life storage medium according to  claim 10 , wherein the ratio of propan-1,2-diol to water is at least 3:1 by volume. 
   
   
       12 . A limited life storage medium according to  claim 8 , wherein the at least one water-soluble reagent is selected from NaOH, KOH, HCl, H 2 SO 4 , HNO 3 , citric acid, CUSO 4 , NaCl, AgNO 3 , AuCl 3 , and combinations thereof. 
   
   
       13 . A limited life storage medium according to  claim 1 , wherein the hygroscopic substance is selected to buffer the amount of water. 
   
   
       14 . A limited life storage medium according to  claim 13 , wherein the hygroscopic substance is selected to buffer the amount of water within a range at which the medium remains flowable through normal variations in the humidity of the ambient atmosphere.